Many persons often listen to music by attaching a tool such as an earphone or a headphone thereto (Hereinafter, the tool is called “earphone”). When they listen to music by attaching the earphone, a sound such as a noise from the outside can be cut. However, a necessary sound (Hereinafter, it is called “information sound”) as information from the outside is out in the same way. Here, for example, the information sound is a call from another person surrounding the listener, a guide voice for guidance, or a warning sound (such as a Klaxon from an automobile). Accordingly, when the listener listens to music with an earphone, even if the outside sound is cut by the earphone, it is desired for the listener not to miss the information sound because of prevention of danger and support of hearing sense.
On the other hand, by amplifying an information sound acquired by a microphone built in the earphone, an acoustic control device to present the information sound to the listener exists. However, a background noise having extremely high level is mixed in sounds from the city. Accordingly, by convoluting the amplified background noise therewith, it is hard for the listener to listen to the music (listening sound) as a listening target.